Patent EA-004972-B1 (EA)
Title: Method and apparatus for clarifying a slurry
Inventor: NYMAN BROR
IPC: B01D21/08
Filed: 2002-06-19
Abstract: 1. A method to clarify and/or thicken a solution containing solids, whereby the slurry is first fed into a feedwell situated in the centre of the upper section of the settling space for clarification, where a flocculant is mixed into the slurry in the said feedwell and from whence the slurry is fed to the settling space and the settled solids or underflow is removed via a discharge port in the centre of the settling space and the clarified solution is removed as an overflow, characterised in that the flocculant and slurry are fed into the feedwell as a gentle flow and are mixed into each other using the feedwell's own mixing element, after which the mixed slurry is guided from the feedwell to the settling space, in the upper part of a underflow layer as a downward directed flow. 2. A method according to claim 1, characterised in that baffles are located on the edge of the feedwell and that the discharge ports in the lower part of the well are placed between the baffles so that the pressure pulses obtained by the mixing element at the point of baffles aid the even outflow of the slurry. 3. A method according to claim 1, characterised in that the outflow speed of the slurry into the settling space is 0.05-0.2 m/s. 4. An apparatus for the clarification and/or thickening of a solution containing solids, where the apparatus comprises a clarification and/or settling tank (1), which is equipped with a feedwell (2) for the slurry to be settled, a discharge port (9) for the settled solids or underflow in the centre of the settling tank, a discharge launder (16) for a clarified solution or overflow, and a rake system (10) rotating on its shaft (11) in order to move the underflow from the edges towards the centre of the tank, characterised in that the feedwell (2) is equipped with a mixing element (3) rotating on its shaft (4), the mixing element (3) is a helix mixer, formed of two tubes (23) attached to a shaft (4) by means of support elements (24), which make 1/3-2 revolutions around the shaft and a guiding cone (5) for the slurry fixed to the lower section of the feedwell, and is comprised of at least one conical surface (31) which is open inside and equipped with slurry guide ports (32). 5. An apparatus according to claim 4, characterised in that the shaft (11) of the settling tank rake is located to go through a shaft (4) of the feedwell mixing element. 6. An apparatus according to claim 4, characterised in that the feedwell (2) is equipped with baffles (26). 7. An apparatus according to claim 6, characterised in that the height of at least some of the baffles (26) is essentially the same as the height of the feedwell (2). 8. An apparatus according to claim 6, characterised in that the height of at least some of the baffles (26) is essentially 1/3 of the height of the feedwell (2). 9. An apparatus according to claim 4, characterised in that the bottom (28) of the feedwell is equipped with slurry discharge ports (29). 10. An apparatus according to claim 12, characterised in that the slurry discharge ports (29) are located between the baffles (24). 11. An apparatus according to claim 4, characterised in that the conical surface (31) of the guiding cone (5) opens downwards at a 45-75 degree angle from the horizontal. 12. An apparatus according to claim 4, characterised in that the guiding cone (5) attached to the lower part of the feedwell is comprised of two conical surfaces (30,31) which are open inside. 13. An apparatus according to claim 12, characterised in that the guiding cone (5) attached to the lower part of the feedwell is comprised of two conical surfaces (31) which are open inside, and of which the upper opens downwards at an a angle of 20-45 degrees from the horizontal and the lower at an angle of 45-75 degrees from the horizontal. 14. An apparatus according to claim 12, characterised in that an essentially vertical lower edge (33) is fixed to the lower conical surface (31) of the guiding cone. 15. An apparatus according to claim 14, characterised in that the diameter of the lower edge (33) of the guiding cone is 1.3-2 times that of the diameter of the feedwell. 16. An apparatus according to claim 12, characterised in that the lowest conical surface is equipped with slurry guide ports (32).